Hyaluronic acid (HA) is a unique glycosaminoglycan. Unlike others, which are synthesized on core proteins in the golgi to form proteoglycans, HA is not assembled on a core protein. Rather, it is synthesized at sites associated with the plasma membrane with the elongating chain being extended into the extracellular matrix. The biological functions of HA in the extracellular matrix are based on the ability of the HA molecules to occupy large hydrodynamic domains and to interact with various specific proteins which constitute structural components in the matrix or are associated with the cell surface. There are conflicting data concerning the nature of the HA synthetase, whether it is a single enzyme or a multi-enzyme complex. Additionally, studies on the regulation of HA synthesis have been technically difficult. The purpose of this project is to study the properties of the HA synthesizing enzyme(s) and the organization and biological roles of HA in the extracellular matrix in model cell culture systems. Topics of current interest include: determination of the mechanism by which newly synthesized HA is organized into a highly viscoelastic network during differentiation of 3T3 L1 cells into adipocytes.